DESCRIPTION: (Applicant's Abstract) A conditioned taste aversion occurs when consumption of a gustatory stimulus is reduced following pairing with an illness-inducing agent such as LiCl. Given that rats will decrease running speed in a runway that leads to a LiCl injection and avoid a location associated with LiCl presentation, the diminished intake is assumed to arise through an association of the taste with the aversive consequences of the illness-inducing agent. Rats also will reduce consumption of a gustatory stimulus when it is paired with the administration of psychoactive drugs, such as morphine, amphetamine, or cocaine. This finding also has been interpreted as a conditioned taste aversion, despite the fact that these psychoactive drugs facilitate running speed in a runway, sustain a conditioned place preference and are self-administered by both rats and humans. The current proposal advances an alternative hypothesis. That is, rats suppress intake of an otherwise palatable gustatory stimulus when paired with a self-administered drug, because of the rewarding, rather than the aversive, properties of the drug. This new analysis, which depends upon a learning phenomenon known as anticipatory contrast, explains many of the discrepancies that exist between suppressed intake induced by toxins and that induced by drugs of abuse. Furthermore, it eliminates the need to postulate aversive effects for these agents. As such, this interpretation provides a unifying theoretical framework for understanding the effects of psychoactive drugs on behavior and, at the same time, exposes a mechanism of comparison between two potent rewards, drugs of abuse and gustatory stimuli.